I put together my new PSA AR pistol kit last night while watching the game. This is the 4th AR I've built, and damn near the only one I haven't marred while doing so (so close!). A while back a bunch of us talked ourselves into purchasing a pair of Knipex pliers. While expensive, what a game changer for assembling an AR! I used them to push the pins on nearly everything. I wrapped the jaws with painter's tape to prevent marring, and taped off sections of the lower receiver I knew were prone to getting messed up. The great thing about the Knipex is that the jaws close parallel to each other, so all you have to do is control the pressure.
Trigger guard housing ears, get the pin started, adjust the pliers till they're just a bit wider than the pin-ears distance and slowly close the jaws. You'll have to adjust the jaw width a couple of times, but once you get the hang of it, you can do that one handed. No marring.
For the bolt catch assembly? My most feared part of the build because it's hard to get the pin started and driven without bunging up the side of the receiver, or worse, bending the ears. Enter Squirrel Daddy punches. They have a recess in them that allows you to insert the pin, and then have very nice control over the pin while gently tapping it into place with a plastic mallet. The punches are short enough that they don't have to be cocked around the end of the receiver. Once the pin is started, you have to work the punch back off carefully or it'll happily draw the pin back out with it. I found that spinning it as I pulled kept it from bringing the pin with it. Adjust the Knipex to the proper width and starting pushing the pin in with complete control. No marring.
Trigger group pins? Here's where my mistake came. I didn't bother taping the sides of the receiver because drifting the pins in is usually straight forward. These fought me for a while till I figured out that one of the Squirrel Daddy punches was the exact same diameter as the pins, so I got everything lined up with the punch, withdrew it enough to get the pin started, and then applied the Knipex. This went great until the very last moment when the pin for the hammer "popped" the last 1/16" or so and I rocked the pliers right into the side of the receiver. So now I have a tiny-tiny marring in the anodization. Not the plier's fault.
The PSA build was fairly straight forward. They shipped a pistol length AR in a full sized box (it was free shipping, but seemed ridiculous). They provided an extra take down pin spring and detent. They bagged up most of the components with their associated parts so while there was some hunting around it was limited.
Squirrel Daddy punches are dirt cheap:
https://www.amazon.com/Squirrel-Daddy-G ... rrel+daddyKnipex pliers are NOT dirt cheap, but you'll never regret buying them:
https://www.amazon.com/Knipex-8603250-1 ... ipex+tools